The chloride-dependent ON-OFF response to illumination recorded with patch electrodes from depolarizing retinal bipolar cells following run-down of the direct photoreceptor input was blocked by 1 mM kynurenic acid or a mixture of 20 micromoles CNQX and AP-7, presumably because these glutamate antagonists suppressed the responses of third-order neurons. Since CNQX alone only blocked about 80% of the chloride-dependent input, it may be assumed that the responses of the presynaptic third-order neurons are mediated by a combination of kainate and NMDA receptors. When run-down of the direct photoreceptor input was prevented by using high-resistance electrodes, the mixture of CNQX and AP-7 increased the amplitude of the inward current elicited by illumination.